Internal combustion engines may include water injection systems that inject water into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions.
As explained above, water may be injected into different locations, including the intake manifold, intake ports of engine cylinders, or directly into engine cylinders. While direct and port injection may provide increased cooling to the engine cylinders and ports, intake manifold injection may increase cooling of the charge air without needing high pressure injectors and pumps. However, due to the lower temperature of the intake manifold, not all the water injected at the intake manifold atomizes properly. Condensed water from water injection may accumulate within the intake manifold and result in unstable combustion if ingested by the engine, Additionally, the inventors herein have recognized that manifold water injection may result in uneven water distribution amongst cylinders coupled to the manifold. For example, water injected upstream of a group of cylinders may not distribute evenly to each of the cylinders due to evaporation, mixing, and entrainment issues, in addition to the airflow maldistribution among cylinders. As a result, uneven cooling may be provided to the engine cylinders.
In one example, the issues described above may be addressed by a method for injecting a first amount of water upstream of a first group of cylinders and a different, second amount of water upstream of a second group of cylinders, the first amount determined based on operating conditions of the first group and the second amount determined based on operating conditions of the second group. Additionally, in one example, injecting the first amount of water may include pulsing a first water injector disposed upstream of the first group of cylinders to deliver the first amount of water. The pulsing may be synchronized to an intake valve opening timing of each cylinder of the first group of cylinders. Further, the first amount of water and/or the pulsing timing may be adjusted based on outputs of knock sensors coupled to each cylinder of the first cylinder group following injection of water. In this way, maldistribution of water between cylinders of a group of cylinders may be identified and the water injection pulses may be adjusted to reduce the variation in water injection amounts between the cylinders. As a result, desired charge air cooling may be provided to each engine cylinder and engine efficiency may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.